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38 Cards in this Set
- Front
- Back
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The spinal cord extends from___ to ___ in adults and to ________ in children.
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Foramen magnum to L1 in adults and to L3 in children.
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Do spinal nerves exit above aor below their respective vertebrae?
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At the cervical level, nerves exit above the vertebrae (thus there are seven cervical vertebrae but 8 cervical nerves). At T1 level and down, nerves exit below their vertebrae.
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What is the cauda equina?
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Because the spinal cord ends at L1, lower nerve roots course some distance before exiting the intervertabral foramina. these lower nerves form the cauda equina (horse's tail).
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Why are spinal injections performed below L1 in an adult (L3 in a child)?
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To avoid potential damage to the spinal cord. Damage to the cauda equina is unlikely as these nerve roots float in the dural sac and tend to be pushed away rather than pierced by an advancing needle.
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Where does the dural sac extend to in adults? In children?
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S2 in adults, S3 in children
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What attaches the terminal end of the spinal cord to the periosteum of the coccyx?
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the filum terminale, an extension of the pia mater, penetrates the dura and and attaches the conus medularis (terminal spinal cord) to the coccyx.
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Anterior spinal arteries: one or two? and supplies 1/3 or 2/3 of the cord's blood supply?
Posterior spinal arteries: one or two? and supplies 1/3 or 2/3 of the cord's blood supply? |
Anterior: one, and supplies the anterior 2/3 of the cords blood supply
Posterior: two, and supplies the posterior 1/3 of the cord's supply. |
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The anterior spinal artery is formed from the ___artery at the _______.
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vertebral artery at the the base of the skull
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The posterior spinal arteries arise from the _____________________.
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posterior inferior cerebral arteries
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The anterior and posterior spinal arteries recieve additional blood flow from the ___________ in the thorax and the ______ in the abdomen.
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intercostal arteries in the thorax
lumbar arteries in the abdomen. |
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The artery of Adamkiewicz is also known as _______________.
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the arteria radicularis magna.
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the artery of adamkiewicz arises from the ________.
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aorta
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The artery of adamkiewicz is unilateral or bilateral?
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unilateral
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Where does the artery of adamkiewicz arise and what does it supply?
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Nearly always arises on the left side off the aorta and provides the major supply to anterior, lower 2/3 of the spinal cord.
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Injury to the artery of adamkiewicz can result in__________?
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spinal artery syndrome.
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The principal site of action for neroaxial blockade is ___.
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The nerve root.
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Why are relatively small doses/volume effective for spinal (subarachnoid ) anesthesia?
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Direct injection onto the CSF
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True of false?
Because of the large volume of LA used in epidural injection, the injection site for epidurals may be distal to the nerve roots that must be anesthetized. |
False. the injection site for epidural anesthesia must be generally close to the nerve roots that must be anesthetized.
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Match:
1) Blockade of neural transmission inthe posterior nerve root. 2) Blockade of neural transmission in the anterior nerve roots. A) somatic and visceral sensation B) efferent motor and autonomic ouflow |
Posterior=somatic and visceral
Anterior =efferent and autonomic |
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What factors influence the effect of LA on nerve fibers?
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-Size of nerve fiber (smaller faster than larger)
-Myelination (myelinated faster than unmyelinated) -Concentration of LA -Duration of contact |
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What is meant by differential blockade?
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sympathetic blockade (judged by temp sensitivity) is 2 segments highrer than sensory (pain, light touch) , which is two segments higher than motor blockade.
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Where is sympathetic outflow from the spinal cord?
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thoracolumbar
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Where is parasmpathetic outflow form the spinal cord?
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craniosacral
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What are B fibers?
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small myelinated preganglionic sympathetic fibers that exit the spinal cord from T1- L2
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Does neuroaxial anesthesia block the vagus nerve? What is the implication of this answer?
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No, the vagus nerve (10th cranial) is not blocked with neuroaxial anesthesia.
Physiologic response to neuroaxial anesthesia result from decreased sympathetic tone or unopposed parasympathetic tone. |
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Vasomotor tone is determined by fibers arising from what level?
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T5-L1
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What is the effect of blocking fibers at T5-L1?
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Loss of vasomotor tone (arterial and venous smoothmuscle)causes vasodilaltion of venous capacitance vessels, pooling of the blood and decreased venous return to the heart. Arterial vasodilation may cause decreased SVR.
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What physiologic effects are you likely to see from a high block and why?
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Profound hypotension, from vasodialtion, bradycardia and decreased contractility. A high sympathetic block may prevent compensatory vasoconstriction above the level of the block, and also may block the cardiac accelerator fibers (T1-T4)
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What level are the cardiac accelerator fibers?
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T1-T4
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What may explain sudden cardiac arrest sometimes seen with spinal anesthesia?
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Unopposed vagal tone.
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How can hypotension be minimized in the face of sympathectomy?
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Volume loading 10-20 ml/kg
Left uterine displacement (in the third trimester) Autotransfusion via T-burg position |
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What pharmacologic agents/classes would be used to treat hypotension/bradycardia of sympathectomy?
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Symptomatic bradycardia: atropine
Hypotension:vasopressors -alpha adrenergic agonists (phenylephrine) increase venous and arterioloar tone -ephedrine has direct Beta adrenergic effects to increase HR nad ctx and indirect effects that produce vasoconstriction Profound hypotension/bradycardia: -epinephrine (5-10 mcg IV) |
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At what levels does the phrenic nerve arise and why is this significant?
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C3,4,5. The phrenic nerve supplies the diaphragm.
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Is the phrenic nerve easily blocked?
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No, the A alpha fibers of the phrenic nerve are quite large. The concentration of LA even with cervical sensory level is reported to be below that needed to block the phrenic nerve. Apnea usually resolves with hemodynamic resuscitation, suggesting hypoperfusion as the causative factor rather than phrenic nerve block.
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Why should neuroaxial blocks be used with caution in patients with severe chronic lung disease?
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High levels of neural blockade will impaire the accessory muscles (intercostal and abdominal) relied on to actively inspire,,exhale or cough.
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What advantages are there to neuroaxial blockade in pts with limited resp reserve?
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Avoidance of airway instrumentation/ positive pressure ventilation.
Thoracic epidural analgesia for POST OP pain control may decrease atelactasis, pneumonia |
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What are the GI manifestations of neuroaxial anesthesia?
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Unopposed vagal tone dominance results in small contracted gut with active peristalsis. Post op epidurals hasten return of GI function.
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What are absolute contraindications to neuroaxial anesthesia?
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Pt refusal
bleeding diathesis severe hypovolemia elevated ICP infection at injection site sebere stenotic valvular disease severe mitral stenosis ventricular outflow obstruction |
